Visible only when SelectionPopup=true. When this is set true, the Flynet Keyboard control will be used to trap the F4 key on the keyboard and use it to trigger the popup.
The use of the F4 key to trigger a selection on a field was originally specified in the Common User Access (CUA) guidelines, co-authored by IBM and Microsoft in the late '80's. It is consistently used in AS400 / iSeries / System i host 5250 applications.
